Substituting definate integrals

I have been having problems substituting and one instance of basic integration. 1 and 3 are subs and 2 is the basic integration (I believe)
1. /int (sqrt pi)_0 x(cos x)^2 the answer is 0
2. /int (x^2)(2x^3)^1/2 the answer is (2/9)(sqrt 2)(x^(9/2))+C
3. /int ((x^2)(2x^3-5)^1/2) the answer is (1/9)(2x^3-5)^3/2+C

For 2. i laid it out as x^2*(2x^3)^1/2. mult. for it to be, just 2x^3 which i know is wrong. plz help.